K.M. Garadkar

Chemical deposition of cubic CdSe and HgSe thin films and their characterization

A modified chemical bath deposition method has been developed to prepare CdSe and HgSe semiconductor thin films in cubic modification, based on the chemical reaction of complexed cadmium acetate, mercuric nitrate with sodium selenosulphate in an aqueous ammoniacal medium at 5 °C. The films were characterized by using x-ray diffraction, optical absorption, electrical measurements and energy dispersive x-ray analysis techniques. The films were uniform, well adherent, dark red and polycrystalline in cubic form without trace of any hexagonality. The CdSe film shows two bandgaps at 2.15 and 1.86 eV, while HgSe shows two bandgaps at 0.8 and 0.45 eV. A thermoelectric study indicated the presence of an n-type conduction mechanism.

Photocatalytic activity of Eu3+-doped ZnO nanorods synthesized via microwave assisted technique

Abstract The doped ZnO nanorods as a photocatalyst with different Eu contents were prepared by microwave assisted method and they were characterized by means of X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), UV-Vis spectroscopy, surface area Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average crystallite size and band gap energy of Eu-doped ZnO were varied with the Eu content. The XRD pattern of Eu-doped ZnO indicated hexagonal crystal structure with an average crystallite size of 25 nm. The presence of europium with trivalent state and its doping successfully into the crystal lattice of ZnO matrix were confirmed by XPS technique. The photocatalytic activity of Eu-doped ZnO nanorods was evaluated for methyl orange degradation. The photocatalytic experiments showed ∼91% degradation of methyl orange over 0.2 mol.% Eu doped ZnO sample within 3 h under UV light (365 nm).

Highly active lanthanum doped ZnO nanorods for photodegradation of metasystox.

La-doped ZnO nanorods with different La contents were synthesized by microwave assisted method and characterized by various sophisticated techniques such as XRD, UV-Vis., EDS, XPS, SEM and TEM. The XRD patterns of the La-doped ZnO indicate hexagonal crystal structure with an average crystallite size of 30nm. It was found that the crystallite size of La-doped ZnO is much smaller as compared to pure ZnO and decreases with increasing La content. The photocatalytic activity of 0.5mol% La-doped ZnO in the degradation of metasystox was studied. It was observed that degradation efficiency of metasystox over La-doped ZnO increases up to 0.5mol% doping then decreases for higher doping levels. Among the catalyst studied, the 0.5mol% La-doped ZnO was the most active, showing high photocatalytic activity for the degradation of metasystox. The maximum reduction of concentration of metasystox was observed under static condition at pH 8. Reduction in the Chemical Oxygen Demand (COD) of metasystox was observed after 150min. The cytotoxicological studies of meristematic root tip cells of Allium cepa were studied. The results obtained indicate that photocatalytically degraded products of metasystox were less toxic as compared to metasystox.

Preparation of N doped TiO2 via microwave-assisted method and its photocatalytic activity for degradation of Malathion

We report herein, nitrogen doped TiO2 nanostructure synthesized by simple microwave assisted method, where ammonia was used as hydrolyzing agent. The synthesized nanomaterials were characterized by means of X-ray diffraction (XRD) which demonstrated that N-doped TiO2 is in anatase phase with average crystallite size of 10nm. Doping of N into the lattice of TiO2 was supported by X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR), CHNS analysis, energy dispersive spectroscopy (EDS). The diffuse reflectance spectroscopy (DRS) showed shifting of absorption edge toward the visible region. Thermogravimetric-differential thermal analysis (TGA-DTA) points out N-doped TiO2 nanoparticles are thermally stable. In order to achieve maximum degradation efficiency, the effect of catalyst loading, pH and light sources (UV and sunlight) were studied. A maximum 97% degradation efficiency was achieved under optimized conditions. A 80% reduction in the chemical oxygen demand (COD) was observed after 150min that indicated mineralization of Malathion. The cytotoxicological studies indicate that photocatalytically degraded products were less toxic as compared to Malathion.

One pot synthesis of magnetite–silica nanocomposites: applications as tags, entrapment matrix and in water purification

We report herein a novel one pot single step synthesis of magnetite–silica nanocomposites. The concept of co-precipitation of iron(II) and iron(III) salts by a base has been used. The main process differentiator is the use of an alkaline solution of sodium silicate instead of a base. This unique modification helps not only in the formation of iron oxide (due to alkaline conditions) but also introduces silica in the reaction to form a magnetite–silica nanocomposite. Having a silica surface is advantageous, in that it stabilizes the silica particles, makes them biocompatible and gives opportunity to further modify and tag functional groups via the well established silica surface chemistry. Furthermore, the process also yields porous silica, which increases the overall surface area of the nanocomposite. The nanocomposite samples have been characterized by a host of techniques, such as UV-vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy dispersive analysis using X-rays (EDAX), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), zeta potential measurements, dynamic light scattering and magnetic measurements. The utility of these high-surface area nanocomposites for different applications such as tagging (attachment of fluorophores Rhodamine, Rh B), entrapment matrix (zinc loading) and removal of arsenic for water purification has been explored.

Template free synthesis of ZnO/Ag2O nanocomposites as a highly efficient visible active photocatalyst for detoxification of methyl orange

A simple and effective route for the synthesis of ZnO/Ag2O nanocomposites with different weight ratios (4:1 to 4:4) have been successfully obtained by combination of thermal decomposition and precipitation technique. The structure, composition, morphology and optical properties of the as-prepared ZnO/Ag2O composites were characterized by XRD, FT-IR, EDS, SEM, TEM, UV-Vis DRS and PL, respectively. The photocatalytic performance of the photocatalysts was evaluated towards the degradation of a methyl orange (MO) under UV and visible light. More specifically, the results showed that the photocatalytic activity with highest rate constant of MO degradation over ZnO/Ag2O (4:2) nanocomposites is more than 22 and 4 times than those of pure ZnO and Ag2O under visible light irradiation, respectively. An improved photocatalytic activity was attributed to the formation of heterostructure between Ag2O and ZnO, the strong visible light absorption and more separation efficiency of photoinduced electron-hole pairs. Moreover, the ZnO/Ag2O (4:2) nanocomposite showed excellent stability towards the photodegradation of MO under visible light. Finally, a possible mechanism for enhanced charge separation and photodegrdation is proposed. Genotoxicity of MO before and after photodegradation was also evaluated by simple comet assay technique.

Biogenic synthesis of multi-applicative silver nanoparticles by using Ziziphus Jujuba leaf extract.

Herein, we are reporting for the first time one step biogenic synthesis of silver nanoparticles (AgNPs) at room temperature by using Ziziphus Jujuba leaf extract as a reducing and stabilizing agent. The process of nanoparticles preparation is green, rapid, environmentally benign and cost effective. The synthesized AgNPs were characterized by means of UV-Vis., XRD, FT-IR, TEM, DLS and Zeta potential. The absorption band centered at λmax 434 nm in UV-Vis. reflects surface plasmon resonance (SPR) of AgNPs. XRD analysis revealed, that biosynthesized AgNPs are crystalline in nature with the face centered cubic structure. FT-IR analysis indicates that nanoparticles were capped with the leaf extract. TEM images shows the synthesized nanoparticles are having different shapes with 20-30 nm size. The data obtained from DLS that support the hydrodynamic size of 28 nm. Zeta potential of -26.4 mV indicates that the nanoparticles were highly stable in colloidal state. The effect of pH, quantity of leaf extract and concentrations of AgNO3 were also studied to attend control over the particle size and stability. The synthesized AgNPs shows highly efficient catalytic activity towards the reduction of anthropogenic pollutant 4-nitrophenol (4-NP) and Methylene Blue (MB) for environmental protection. Synthesized AgNPs also exhibited good antimicrobial activity against Escherichia coli.

CdHgSe thin films: preparation, characterization and optoelectronic studies

We present a modified chemical bath deposition method used to grow Cd1−xHgxSe (0 < x < 1) pseudo-binary thin films with the objective to study growth kinetics, structural, optical and electrical changes. The method is based on the reaction of CdSO4, Hg(NO3)2 and Na2SeSO3 in an aqueous ammonical medium at a temperature of 5 °C. The reactant concentration, pH, deposition temperature and rate of agitation were found to influence significantly the quality and thickness of the films. The as-deposited thin films were characterized by x-ray diffraction (XRD), atomic absorption spectrophotometry, scanning electron microscopy, optical absorption and thermoelectrical techniques. The XRD study confirms the polycrystalline nature in a single cubic phase over the whole range of composition studied. The grain size is found to be similar for all compositions. An analysis of absorption spectra gave a direct type optical bandgap, the magnitude of which decreases monotonically as mercury content (x) in the film is increased while dark dc electrical conductivity at room temperature was found to increase nonlinearly from 10−6 to 102 Ω−1 cm−1. All the films showed n-type conductivity. The main features observed are the formation of continuous solid solutions in a single cubic phase, the absence of other crystallographic phases, the lack of solubility gap, and stability.

Morphological and optoelectronic studies on poly-crystalline leaf-like cobalt selenide thin film synthesized using a chemical bath deposition technique

The inorganic material cobalt selenide (CoSe), in crystalline form, possesses an optimal band gap matchable to the maximum of the solar spectrum, a high optical absorption coefficient and good conductivity. These characteristics make it quite suitable for use as a photo-electrode in solar conversion devices. However, it is difficult to obtain crystalline, uniform and stoichiometric deposits by conventional methods due to the large difference in their melting points. In view of this, we present a facile, low temperature chemical bath deposition route for the synthesis of highly ordered cobalt selenide thin films. Cobalt nitrate, sodium selenosulphate and ammonia were employed for the synthesis. The films were characterized using X-ray diffraction, optical absorbance, photoluminescence, electrical conductivity, scanning electron microscopy and EDS techniques. The analysis revealed a poly-crystalline structure in a stoichiometric, cubic form with a leaf-like morphology. The size and shape of the ‘leaf’ structure was observed to be uniform. A band gap of 1.7 eV was observed. The room temperature photoluminescence spectra displayed a strong, symmetrical peak at 1.7 eV confirming the directness of the band gap, while the conductivity measurements confirmed the semiconducting nature of the film with a single type of conduction mechanism. As per our literature survey on the chemical synthesis, this is the first attempt for the synthesis of poly-crystalline CoSe in thin film form.

Cetyltrimethylammonium bromide stabilized perylene nanoparticles for fluorimetric estimation of bicarbonate (HCO3−) anion: spectroscopic approach

Fluorescent perylene nanoparticles were prepared by a reprecipitation method in the presence of cetyltrimethylammonium bromide (CTAB) as a stabilizer. The formation of perylene nanoparticles was confirmed by dynamic light scattering , UV-visible absorption spectroscopy, fluorescence spectroscopy and excited state life time measurements. The observation of a significant large Stokes shift (24 546 cm−1) of perylene nanoparticles in aqueous suspension as compared with that of a dilute solution of perylene in acetone (14 250 cm−1) indicated aggregation of molecules in their ground state by lateral π-stacking. A highly intense, single band fluorescence peak at 565 nm is attributed to the direct excitation of perylene nanoparticles (λex = 380 nm) due to aggregation induced enhanced emission (AIEE) and is quenched appreciably by HCO3− anions. A positive surface charge is created by the CTAB cage on the nanoparticles and binding interactions result in quenching of fluorescence of perylene nanoparticles which is observed in the spectrum at 565 nm. The quenching of perylene nanoparticles emission is linear in the concentration range of 0–80 μM of HCO3− ion in solution. The quenching results obey the Stern–Volmer relation and the method after calibration can be applied successfully in the quantitative analysis of sodium bicarbonate in commercially available medicinal tablets.